From bb7f68d633e4a353174c8b96c6d860a9a96612a4 Mon Sep 17 00:00:00 2001
From: Braiden Vasco <braiden-vasco@users.noreply.github.com>
Date: Sun, 5 Nov 2017 09:50:04 +0000
Subject: [PATCH] Add module "syscall"

---
 arch/Makefile    |  1 +
 arch/config.h    |  2 ++
 arch/protected.c |  7 ++++---
 arch/syscall.asm | 32 ++++++++++++++++++++++++++++++++
 arch/syscall.c   | 14 ++++++++++++++
 arch/syscall.h   |  6 ++++++
 6 files changed, 59 insertions(+), 3 deletions(-)
 create mode 100644 arch/syscall.asm
 create mode 100644 arch/syscall.c
 create mode 100644 arch/syscall.h

diff --git a/arch/Makefile b/arch/Makefile
index 196f1a8..0bda5c8 100644
--- a/arch/Makefile
+++ b/arch/Makefile
@@ -19,6 +19,7 @@ OBJS += kprintf.c.o
 OBJS += protected.c.o protected.asm.cpp.o
 OBJS += exception.c.o exception.asm.cpp.o
 OBJS += hwint.c.o     hwint.asm.cpp.o
+OBJS += syscall.c.o   syscall.asm.cpp.o
 
 OBJS += timer.c.o
 
diff --git a/arch/config.h b/arch/config.h
index d423a67..a345759 100644
--- a/arch/config.h
+++ b/arch/config.h
@@ -38,4 +38,6 @@
 #define INT_HWINT_FIRST (INT_EXCEPTION_LAST + 1)
 #define INT_HWINT_LAST  (INT_HWINT_FIRST + INT_HWINT_COUNT - 1)
 
+#define INT_SYSCALL 0x80
+
 #endif
diff --git a/arch/protected.c b/arch/protected.c
index 06f27be..e41046b 100644
--- a/arch/protected.c
+++ b/arch/protected.c
@@ -5,6 +5,7 @@
 #include "asm.h"
 #include "exception.h"
 #include "hwint.h"
+#include "syscall.h"
 
 #include <kernelmq/stdlib.h>
 
@@ -129,6 +130,8 @@ void protected_initialize()
     idt_set_gate(46, (unsigned int)hwint_14, 0x08, 0x8E);
     idt_set_gate(47, (unsigned int)hwint_15, 0x08, 0x8E);
 
+    idt_set_gate(INT_SYSCALL, (unsigned int)syscall_gate, 0x08, 0x8E | 0x60);
+
     logger_info("Load GDT.");
 
     gdt_pointer.limit = sizeof(struct GdtEntry) * GDT_SIZE - 1;
@@ -168,7 +171,5 @@ void idt_set_gate(unsigned char num, unsigned int base, unsigned short sel, unsi
     idt_entries[num].base_hi = (base >> 16) & 0xFFFF;
     idt_entries[num].sel     = sel;
     idt_entries[num].always0 = 0;
-    // We must uncomment the OR below when we get to using user-mode.
-    // It sets the interrupt gate's privilege level to 3.
-    idt_entries[num].flags   = flags /* | 0x60 */;
+    idt_entries[num].flags   = flags;
 }
diff --git a/arch/syscall.asm b/arch/syscall.asm
new file mode 100644
index 0000000..a39a8c0
--- /dev/null
+++ b/arch/syscall.asm
@@ -0,0 +1,32 @@
+#include "config.h"
+
+[EXTERN syscall_handler]
+
+[GLOBAL syscall_gate]
+
+syscall_gate:
+    cli
+
+    pusha ; Pushes edi,esi,ebp,esp,ebx,edx,ecx,eax
+
+    mov ax, ds ; Lower 16-bits of eax = ds.
+    push eax ; save the data segment descriptor
+
+    mov ax, GDT_KERNEL_DS_SELECTOR
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+
+    call syscall_handler
+
+    pop eax ; reload the original data segment descriptor
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+
+    popa                     ; Pops edi,esi,ebp...
+
+    sti
+    iret ; pops 5 things at once: CS, EIP, EFLAGS, SS, and ESP
diff --git a/arch/syscall.c b/arch/syscall.c
new file mode 100644
index 0000000..22feb53
--- /dev/null
+++ b/arch/syscall.c
@@ -0,0 +1,14 @@
+#include "kprintf.h"
+
+struct IsrRegisters {
+    unsigned int ds;                                     // Data segment selector
+    unsigned int edi, esi, ebp, esp, ebx, edx, ecx, eax; // Pushed by pusha.
+    unsigned int eip, cs, eflags, useresp, ss;           // Pushed by the processor automatically.
+};
+
+void syscall_handler(struct IsrRegisters regs)
+{
+    const unsigned int id = regs.eax;
+
+    kprintf("syscall %u\n", id);
+}
diff --git a/arch/syscall.h b/arch/syscall.h
new file mode 100644
index 0000000..1cea0b4
--- /dev/null
+++ b/arch/syscall.h
@@ -0,0 +1,6 @@
+#ifndef KERNELMQ_INCLUDED_SYSCALL
+#define KERNELMQ_INCLUDED_SYSCALL 1
+
+void syscall_gate();
+
+#endif